U.S. patent application number 12/810041 was filed with the patent office on 2010-10-21 for acicular boehmite nanoparticles.
Invention is credited to Brant U. Kolb, Grant F. Tiefenbruck, Thomas E. Wood.
Application Number | 20100267881 12/810041 |
Document ID | / |
Family ID | 41017174 |
Filed Date | 2010-10-21 |
United States Patent
Application |
20100267881 |
Kind Code |
A1 |
Tiefenbruck; Grant F. ; et
al. |
October 21, 2010 |
ACICULAR BOEHMITE NANOPARTICLES
Abstract
Acicular boehmite nanoparticles, methods of making acicular
boehmite nanoparticles, and composite materials that contain
acicular boehmite nanoparticles are described. The acicular
boehmite nanoparticles are prepared in a continuous hydrothermal
reactor from a feedstock solution containing a soluble
aluminum-containing precursor.
Inventors: |
Tiefenbruck; Grant F.;
(Cottage Grove, MN) ; Kolb; Brant U.; (Afton,
MN) ; Wood; Thomas E.; (Stillwater, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Family ID: |
41017174 |
Appl. No.: |
12/810041 |
Filed: |
December 17, 2008 |
PCT Filed: |
December 17, 2008 |
PCT NO: |
PCT/US08/87077 |
371 Date: |
June 22, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61017267 |
Dec 28, 2007 |
|
|
|
Current U.S.
Class: |
524/437 ;
423/626; 428/403; 977/773 |
Current CPC
Class: |
C07F 5/069 20130101;
Y10T 428/2991 20150115 |
Class at
Publication: |
524/437 ;
423/626; 428/403; 977/773 |
International
Class: |
C08K 3/18 20060101
C08K003/18; C01F 7/00 20060101 C01F007/00 |
Claims
1. A method of making an acicular boehmite nanoparticle, the method
comprising: providing a feedstock solution comprising an
aluminum-containing precursor dissolved in an aqueous-based solvent
at a pH no greater than 6, the aluminum-containing precursor being
of Formula (I)
Al(OH).sub.w(R.sup.1).sub.x(R.sup.2).sub.y(R.sup.3).sub.z (I)
wherein R.sup.1 is a first carboxylate selected from a formate or
acetate; R.sup.2 is a second carboxylate that is different from the
first carboxylate and that is selected from acetate, propionate,
butyrate, or mixtures thereof; R.sup.3 is an optional third
mono-carboxylate having at least 5 carbon atoms; w+x+y+z=3; w is in
a range of 1.5 to 2.2; x is equal to at least 0.1; y is equal to at
least 0.1; and z is in a range of 0 to 0.2; and passing the
feedstock solution through a continuous hydrothermal reactor,
wherein an effluent of the continuous hydrothermal reactor
comprises the acicular boehmite nanoparticle.
2. The method of claim 1, wherein R.sup.1 is formate and R.sup.2 is
acetate, propionate, or a mixture thereof.
3. The method of claim 1, wherein x is in the range of 0.5 to 1.3
and y is in the range of 0.2 to 1.0.
4. The method of claim 1, wherein the feedstock solution contains
the aluminum-containing precursor in an amount in a range of 0.1 to
5 molar.
5. The method of claim 1, wherein the effluent further comprises
(a) a dissolved first carboxylic acid, a dissolved anion of the
first carboxylic acid, or a mixture thereof wherein the first
carboxylic acid is selected from formic acid or acetic acid, and
(b) a dissolved second carboxylic acid, a dissolved anion of the
second carboxylic acid, or a mixture thereof wherein the second
carboxylic acid is different than the first carboxylic acid and is
selected from acetic acid, propionic acid, butyric acid, or a
mixture thereof.
6. The method of claim 5, further comprising removing at least a
portion of (a) the dissolved first carboxylic acid, the dissolved
anion of the first carboxylic acid, or a mixture thereof, and at
least a portion of (b) the dissolved second carboxylic acid, the
dissolved anion of the second carboxylic acid, or a mixture
thereof.
7. The method of claim 1, further comprising adding a surface
modifying agent to a surface of the acicular boehmite
nanoparticle.
8. The method of claim 1, further comprising removing at least a
portion of an aqueous-based solvent from the effluent.
9. The method of claim 1, further comprising dispersing or
suspending the acicular boehmite nanoparticle in an organic
matrix.
10. The method of claim 1, wherein the feedstock solution further
comprises (a) a mono-carboxylic acid having a polyalkylene oxide
group or (b) an alpha-hydroxyl carboxylic acid having a single
carboxyl group.
11. The method of claim 1, wherein the continuous hydrothermal
reactor comprises a heated tubular reactor.
12. The method of claim 11, wherein an interior of the tubular
reactor is lined with a fluorinated polymeric material.
13. The method of claim 12, wherein the polymeric material
comprises a fluorinated polyolefin.
14. The method of claim 1, wherein R.sup.3 is mono-carboxylate
comprising a poly(alkylene oxide) group.
15. A material comprising an acicular boehmite nanoparticle,
wherein multiple sorbed modifiers are on a surface of the acicular
boehmite nanoparticle, the sorbed modifiers comprising (a) a first
carboxylic acid, an anion of the first carboxylic acid, or a
mixture thereof, wherein the first carboxylic acid is selected from
formic acid or acetic acid; and (b) a second carboxylic acid, an
anion of the second carboxylic acid, or a mixture thereof, wherein
the second carboxylic acid is different than the first carboxylic
acid and wherein the second carboxylic acid is selected from acetic
acid, formic acid, propionic acid, butyric acid, or a mixture
thereof.
16. The material of claim 15, wherein the acicular boehmite
nanoparticle has an average aspect ratio of at least 3:1.
17. The material of claim 15, the first carboxylic acid is formic
acid and the second carboxylic acid is acetic acid, propionic acid,
or a mixture thereof.
18. The material of claim 15, further comprising (c) a third
carboxylic acid, an anion of the third carboxylic acid, or a
mixture thereof, wherein the third carboxylic acid is a
mono-carboxylic acid comprising a poly(alkylene oxide) group.
19. A composite material comprising an organic matrix and acicular
boehmite nanoparticle dispersed in the organic matrix, wherein
multiple sorbed modifiers are on a surface of the acicular boehmite
nanoparticle, the sorbed modifiers comprising (a) a first
carboxylic acid, an anion of the first carboxylic acid, or a
mixture thereof, wherein the first carboxylic acid is selected from
formic acid or acetic acid; and (b) a second carboxylic acid, an
anion of the second carboxylic acid, or a mixture thereof, wherein
the second carboxylic acid is different than the first carboxylic
acid and wherein the second carboxylic acid is selected from acetic
acid, formic acid, propionic acid, butyric acid, or a mixture
thereof.
20. The composite material of claim 19, further comprising (c) a
third carboxylic acid, an anion of the third carboxylic acid, or a
mixture thereof, wherein the third carboxylic acid is a
mono-carboxylic acid comprising a poly(alkylene oxide) group.
21. The composite material of claim 19, further comprising an
additional surface modification agent sorbed on a surface of the
acicular boehmite nanoparticles.
Description
TECHNICAL FIELD
[0001] This invention relates to acicular boehmite nanoparticles,
methods of making acicular boehmite nanoparticles, and composite
materials that contain acicular boehmite nanoparticles.
BACKGROUND
[0002] Methods of making boehmite are known. Many of these methods,
however, do not produce boehmite that is acicular or that is in the
nanoparticle size range. Some methods that are known for preparing
acicular boehmite require excessively long heating times such as
several hours to several days.
SUMMARY
[0003] The present invention provides acicular boehmite
nanoparticles and methods of making acicular boehmite
nanoparticles. The acicular boehmite nanoparticles have an average
length that is no greater than 1000 nanometers. The nanoparticles
are usually crystalline and substantially non-associated. The
acicular boehmite nanoparticles can be added to an organic matrix
material for a variety of purposes such as, for example, improving
the tensile strength of a polymeric material or thickening an
organic matrix.
[0004] In one aspect, a method of making an acicular boehmite
nanoparticle is provided. The method includes providing a feedstock
solution that includes an aluminum-containing precursor dissolved
in an aqueous-based solvent at a pH no greater than 6. The
aluminum-containing precursor is of Formula (I).
Al(OH).sub.w(R.sup.1).sub.x(R.sup.2).sub.y(R.sup.3).sub.z (I)
In Formula (I), R.sup.1 is a first carboxylate selected from
formate or acetate. Group R.sup.2 is a second carboxylate that is
different than the first carboxylate and that is selected from
acetate, propionate, butyrate, or mixtures thereof. Group R.sup.3
is an optional third mono-carboxylate having at least 5 carbon
atoms. The sum of the variables w, x, y, and z is equal to 3 with w
being in the range of 1.5 to 2.2, x being at least 0.1, y being at
least 0.1, and z being in the range of 0 to 0.2. The method further
includes passing the feedstock solution through a continuous
hydrothermal reactor. An effluent of the continuous hydrothermal
reactor contains the acicular boehmite nanoparticle.
[0005] In another aspect, an acicular boehmite nanoparticle is
provided. Various sorbed modifiers are on a surface of the acicular
boehmite nanoparticle. The sorbed modifiers include (a) a first
carboxylic acid, an anion of the first carboxylic acid, or a
mixture thereof and (b) a second carboxylic acid, an anion of the
second carboxylic acid, or a mixture thereof. The first carboxylic
acid is selected from formic acid or acetic acid. The second
carboxylic acid, which is different than the first carboxylic acid,
is selected from acetic acid, formic acid, propionic acid, butyric
acid, or a mixture thereof.
[0006] In yet another aspect, a composite material is provided that
includes an organic matrix and an acicular boehmite nanoparticle
dispersed or suspended in the organic matrix. Various sorbed
modifiers are on a surface of the acicular boehmite nanoparticle.
The sorbed modifiers include (a) a first carboxylic acid, an anion
of the first carboxylic acid, or a mixture thereof and (b) a second
carboxylic acid, an anion of the second carboxylic acid, or a
mixture thereof. The first carboxylic acid is selected from formic
acid or acetic acid. The second carboxylic acid, which is different
than the first carboxylic acid, is selected from acetic acid,
formic acid, propionic acid, butyric acid, or a mixture
thereof.
[0007] The above summary of the present invention is not intended
to describe each disclosed embodiment or every implementation of
the present invention. The Figure, Detailed Description and
Examples that follow more particularly exemplify these
embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The invention may be more completely understood in
consideration of the following detailed description of various
embodiments of the invention in connection with the accompanying
drawings, in which:
[0009] FIG. 1 schematically illustrates an exemplary continuous
hydrothermal reactor system.
[0010] FIG. 2 shows an exemplary transmission electron micrograph
of the acicular boehmite nanoparticle.
[0011] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the
invention.
DETAILED DESCRIPTION
[0012] Acicular boehmite nanoparticles, methods of making acicular
boehmite nanoparticles, and composite materials that contain
acicular boehmite nanoparticles are described. The acicular
boehmite nanoparticles, which are prepared in a continuous
hydrothermal reactor, typically have an average length no greater
than 1000 nanometers and an average aspect ratio equal to at least
3:1.
[0013] As used herein, the term "organic matrix" refers to a
polymeric material or a precursor (e.g., monomer or oligomer) to a
polymeric material. That is, the organic matrix can contain
polymerized material, polymerizable material, or a mixture
thereof.
[0014] In one aspect, a method of making an acicular boehmite
nanoparticle is provided. The method includes providing a feedstock
solution containing an aluminum-containing precursor dissolved in
an aqueous-based solvent at a pH no greater than 6. The feedstock
solution is passed through a continuous hydrothermal reactor. The
aluminum-containing precursor undergoes hydrolysis and condensation
reactions within the continuous hydrothermal reactor that result in
the formation of the acicular boehmite nanoparticle.
[0015] As used herein, the term "continuous hydrothermal" refers to
a method of heating an aqueous medium at a temperature above the
normal boiling point of the aqueous medium at a pressure that is
equal to or greater than the pressure required to prevent boiling
of the aqueous medium. A feedstock is continually introduced into a
heated zone and an effluent is continually removed from the heated
zone of the continuous hydrothermal rector. The continual
introduction of the feedstock and continual removal of the effluent
can be constant or intermittent (e.g., pulsed). The introduction of
the feedstock and the removal of the effluent typically occur in
different regions of the heated zone.
[0016] As used herein, the term "boehmite" refers to a material
that is predominantly gamma-aluminum oxy hydroxide
(.gamma.-AlOOH).
[0017] The aluminum-containing precursor that is dissolved in the
feedstock solution for the continuous hydrothermal continuous
reactor is of Formula (I).
Al(OH).sub.w(R.sup.1).sub.x(R.sup.2).sub.y(R.sup.3).sub.z (I)
[0018] In Formula (I), R.sup.1 is a first carboxylate selected from
formate or acetate. Group R.sup.2 is a second carboxylate that is
different than the first carboxylate and that is selected from
acetate, propionate, butyrate, or a mixture thereof. Group R.sup.3
is an optional third mono-carboxylate having at least 5 carbon
atoms. The sum of the variables w, x, y, and z is equal to 3 with w
being in the range of 1.5 to 2.2, x being at least 0.1, y being at
least 0.1, and z being in the range of 0 to 0.2.
[0019] The aluminum-containing precursor of Formula (I) can be
prepared by any known process. In many embodiments, this
aluminum-containing precursor is prepared by digesting aluminum
metal in a mixture of water and at least two different carboxylic
acids. At least two of the carboxylic acids are mono-carboxylic
acids (i.e., the carboxylic acids each have a single carboxyl
group) having 1 to 4 carbon atoms. A first carboxylic acid is
usually formic acid or acetic acid. A second carboxylic acid, which
is different than the first carboxylic acid, is usually acetic
acid, propionic acid, butyric acid, or a mixture thereof. An
optional third mono-carboxylic acid can contain at least 5 carbon
atoms. In some embodiments, the first carboxylic acid is formic
acid, the second carboxylic acid is acetic acid, propionic acid,
butyric acid, or a mixture thereof, and there is no third
carboxylic acid having at least 5 carbon atoms.
[0020] The optional third carboxylic acid having at least 5 carbon
atoms is often a mono-carboxylic acid having a poly(alkylene oxide)
group. The third carboxylic acid often has up to 30 carbon atoms,
up to 20 carbon atoms, up to 18 carbon atoms, up to 16 carbon
atoms, up to 14 carbon atoms, or up to 12 carbon atoms. For
example, the third carboxylic acid can be of Formula (II).
R.sup.4--(OR.sup.5).sub.n--COOH (II)
In Formula (II), R.sup.4 is an alkyl group having 1 to 4 carbon
atoms, R.sup.5 is an alkylene group having 1 to 4 carbon atoms, and
the variable n is an integer in the range of 1 to 10.
[0021] For example, the third carboxylic acid can be, but is not
limited to, 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEAA) and
2-(2-methoxyethoxy)acetic acid (MEAA).
[0022] Stated differently, the optional group R.sup.3 in Formula
(I) is often a mono-carboxylate having a poly(alkylene oxide group.
Groups R.sup.3 often has 5 to 30 carbon atoms, 5 to 20 carbon
atoms, 5 to 16 carbon atoms, or 5 to 12 carbon atoms. In some
embodiment, R.sup.3 is of Formula (III)
R.sup.4--(OR.sup.5).sub.n--COO.sup.- (III)
where R.sup.4 and R.sup.5 are the same as defined for Formula (II).
Exemplary R.sup.3 groups include, but are not limited to,
2-[2-(2-methoxyethoxy)ethoxy]acetate and
2-(2-methoxyethoxy)acetate.
[0023] The digestion mixture for preparing the aluminum-containing
precursor of Formula (I) is usually heated in the range of
70.degree. C. to 100.degree. C. for at least 1 hour, at least 2
hours, at least 4 hours, at least 6 hours, at least 8 hours, or at
least 10 hours. A reflux condenser is often used to minimize the
loss of any of the carboxylic acids or water. The reaction is
typically terminated when hydrogen evolution ceases from the
digestion mixture and no aluminum metal is visible within the
digestion mixture.
[0024] The amount of aluminum, first carboxylic acid, second
carboxylic acid, and optional third carboxylic acid in the
digestion mixture can be selected to produce the desired
aluminum-containing precursor of Formula (I). Further, the total
concentration of aluminum-containing precursor formed can be varied
by altering the concentration of the reactants added to the
digestion mixture.
[0025] The concentration of aluminum metal added to the digestion
mixture is usually greater than 0.1 molar. If lower concentrations
are used, the amount of the precursor formed may be unacceptably
low and a concentration step may be needed prior to being used as
the feedstock solution for the continuous hydrothermal reactor. The
concentration of aluminum metal is often at least 0.2 molar, at
least 0.5 molar, at least 0.75 molar, at least 1.0 molar, at least
1.25 molar, at least 1.5 molar, at least 1.75 molar, or at least
2.0 molar. The aluminum metal concentration in the digestion
mixture can be up to 5 molar or greater. If the concentration is
too high, however, the viscosity of the digestion mixture may be
unacceptably high for good mixing. The aluminum metal concentration
often can be up to 4 molar, up to 3 molar, or up to 2 molar. In
some digestion mixtures, the aluminum metal concentration is in the
range of 0.1 to 5 molar, in the range of 0.5 to 5 molar, in the
range of 0.5 to 4 molar, in the range of 0.5 to 3 molar, or in the
range of 0.5 to 2 molar.
[0026] For every mole of aluminum metal added to the digestion
mixture, the total amount of carboxylic acid is typically in the
range of 0.8 to 1.5 moles. That is, for every mole of aluminum
added, there is often a total of 0.8 to 1.5 moles of the first
carboxylic acid plus the second carboxylic acid plus the optional
third carboxylic acid. In some examples, the total amount of
carboxylic acid is in the range of 0.9 to 1.5 moles, in the range
of 1.0 to 1.5 moles, or in the range of 1.0 to 1.4 moles per mole
of aluminum.
[0027] For every mole of aluminum metal added to the digestion
metal, at least 0.1 moles of the first carboxylic acid is typically
added. In many embodiments, at least 0.2 moles, at least 0.3 moles,
at least 0.4 moles, at least 0.5 moles, at least 0.6 moles, at
least 0.7 moles, at least 0.8 moles, at least 0.9 moles, or at
least 1.0 moles of the first carboxylic acid are added for every
mole of aluminum metal present in the digestion mixture. For
example, the amount of the first carboxylic acid can be in the
range of 0.1 to 1.4 moles, in the range of 0.2 to 1.4 moles, in the
range of 0.3 to 1.3 moles, in the range of 0.4 to 1.3 moles, in the
range of 0.5 to 1.3 moles, in the range of 0.5 to 1.2 moles, or in
the range of 0.5 to 1.0 moles per mole of aluminum metal.
[0028] There is typically at least 0.1 mole of the second
carboxylic acid per mole of aluminum present in the digestion
mixture. In many embodiments, at least 0.2 moles, at least 0.3
moles, at least 0.4 moles, or at least 0.5 moles of the second
carboxylic acid are present per mole of aluminum metal in the
digestion mixture. For example, the amount of the second carboxylic
acid can be in the range of 0.1 to 1.4 moles, in the range of 0.2
to 1.4 moles, in the range of 0.2 to 1.2 moles, in the range of 0.2
to 1.0 moles, or in the range of 0.2 to 0.8 moles per mole of
aluminum metal.
[0029] There is generally no more than 0.2 mole of the third
carboxylic acid per mole of aluminum metal in the digestion metal.
The third carboxylic acid can decrease the solubility of the
aluminum-containing precursor in the feedstock for the continuous
hydrothermal reactor but may advantageously improve the
compatibility of the resulting acicular boehmite nanoparticles with
an organic matrix. In some embodiments, however, there is no third
carboxylic acid added to the digestion mixture.
[0030] In some exemplary digestion mixtures, the aluminum
concentration is in the range of 0.1 to 5 molar, the first
carboxylic acid is present in an amount in the range of 0.1 to 1.4
moles per mole of aluminum, and the second carboxylic acid is
present in an amount in the range of 0.1 to 1.4 moles per mole of
aluminum. For example, the aluminum concentration can be in the
range of 0.5 to 3 molar, the first carboxylic acid can be present
in an amount in the range of 0.3 to 1.3 moles per mole of aluminum,
and the second carboxylic acid can be present in an amount in the
range of 0.2 to 1.2 moles per mole of aluminum. In other examples,
the aluminum concentration can be in the range of 0.5 to 3 molar,
the first carboxylic acid can be present in an amount in the range
of 0.5 to 1.3 moles per mole of aluminum, and the second carboxylic
acid can be present in an amount in the range of 0.2 to 1.0 moles
per mole of aluminum. In any of these examples, there can be an
optional third carboxylic acid in an amount up to 0.2 moles per
mole of aluminum.
[0031] Expressed in terms of the aluminum-containing precursor of
Formula (I), w is in the range of 1.5 to 2.2, x is in the range of
0.1 to 1.4, y is in the range of 0.1 to 1.4, and z is in the range
of 0 to 0.2. In some examples, x is in the range of 0.3 to 1.3, y
is in the range of 0.2 to 1.2, and z is in the range of 0 to 0.2.
In other examples, x is in the range of 0.5 to 1.3, y is in the
range of 0.2 to 1.0, and z is in the range of 0 to 0.2.
[0032] In some more specific examples, the aluminum concentration
is in the range of 0.5 to 3 molar, the first carboxylic acid is
formic acid that is present in an amount in the range of 0.5 to 1.3
moles per mole of aluminum, and the second carboxylic acid is
acetic acid, propionic acid, or a mixture thereof that is present
in an amount in the range of 0.2 to 1.0 moles per mole of aluminum.
If a third carboxylic acid is present, it is present in an amount
no greater than 0.2 moles per mole of aluminum. These specific
examples correspond to an aluminum-containing precursor of Formula
(I) where w is in the range of 1.5 to 2.2, x is in the range of 0.5
to 1.3, y is in the range of 0.2 to 1.0, and z is in the range of 0
to 0.2.
[0033] After digestion of the aluminum metal to prepare the
aluminum-containing precursor of Formula (I), the digestion product
is typically cooled to room temperature. The digestion product can
be used directly as the feedstock solution for the continuous
hydrothermal reactor. Alternatively, the digestion product can be
diluted with water (e.g., deionized water) to lower the percent
solids for use as the feedstock solution. Either with or without
further dilution of the digestion product, the feedstock used for
the continuous hydrothermal reactor typically is a solution. That
is, the aluminum-containing precursor of Formula (I) is dissolved
(i.e., not suspended or dispersed) in the feedstock solution.
[0034] Further, there is usually no aluminum-containing particulate
matter included in the feedstock solution. If particles were in the
feedstock, these particles may need to dissolve and then
simultaneously undergo hydrolysis and condensation within the
hydrothermal reactor. Such a process can be difficult to control
because the rate of dissolution will depend on the size of the
particles, the crystalline structure of the particles, and the
surface characteristics of the particles in the feedstock. It can
be difficult to control all of these parameters to prepare a
consistent product. In contrast, a feedstock that is a solution can
be easier to control and reproduce over time. That is, the product
produced in the hydrothermal reactor can be more consistent over
time when a feedstock solution is used. Additionally, the effluent
of the hydrothermal reactor tends to contain fewer types of
materials when a feedstock solution is used compared to when a
feedstock containing particles is used.
[0035] In some embodiments, there can be a small amount of
undissolved residue in the feedstock solution as prepared. This
undissolved residue is often removed before the feedstock solution
is passed through the continuous hydrothermal reactor. For example,
the feedstock solution can be passed through one or more filters.
Any known filter that can remove the undissolved residue can be
used. In some embodiments, a paper filter such as those
commercially available from Whatman International Ltd. (Maidstone,
England) can be used. For example, paper filters such as a Whatman
No. 50 filter or a Whatman No. 54 filter can be used for removing
any undissolved residue. The feedstock solution can be passed
through the filter by applying pressure or by drawing a vacuum on
the receiving vessel.
[0036] The concentration of the feedstock solution is often
expressed based on the aluminum concentration. The aluminum
concentration of the feedstock solution is typically no greater
than 5 molar. Higher concentrations can be difficult to pump
through the continuous hydrothermal reactor. Additionally, more
concentrated feedstocks are more likely to result in the deposition
of materials on the walls of the continuous hydrothermal reactor
leading to restricted flow through the reactor. This type of
deposition can be minimized, however, by using a continuous
hydrothermal reactor with a larger internal diameter or by using a
longer continuous hydrothermal reactor at a higher flow rate. The
aluminum concentration is often no greater than 4 molar, no greater
than 3 molar, no greater than 2 molar, or no greater than 1
molar.
[0037] The concentration of aluminum in the feedstock solution is
often selected to be as high as possible to maximize the efficiency
of the process. In many embodiments, the concentration of aluminum
is no less than 0.1 molar, no less than 0.2 molar, no less than 0.3
molar, no less than 0.4 molar, or no less than 0.5 molar. For
example, the aluminum concentration is often in the range of 0.1 to
5 molar, in the range of 0.2 to 4 molar, in the range of 0.3 to 3
molar, in the range of 0.3 to 2 molar, in the range of 0.5 to 3
molar, or in the range of 0.5 to 2 molar.
[0038] The feedstock solution contains the aluminum-containing
precursor of Formula (I) in an aqueous-based solvent. As used
herein, the term "aqueous-based solvent" means that the solvent
contains water and often is predominantly water. In addition to
water, the aqueous-based solvent can contain, for example, a
water-miscible solvent such as polar organic solvent as well as
various dissolved carboxylic acids, anions of these dissolved
carboxylic acids, or a mixture thereof. For example, the feedstock
solution may contain dissolved carboxylic acids and/or anions
thereof corresponding to those used to prepare the
aluminum-containing precursor of Formula (I). That is, the
feedstock solution may contain (a) a first carboxylic acid, an
anion of the first carboxylic acid, or a mixture thereof and (b) a
second carboxylic acid, an anion of the second carboxylic acid, or
a mixture thereof. The first carboxylic acid is formic acid or
acetic acid and the second carboxylic acid is acetic acid,
propionic acid, butyric acid, or a mixture thereof. The first
carboxylic acid is different than the second carboxylic acid. An
optional third carboxylic acid having at least 5 carbon atoms, an
anion of the optional third carboxylic acid, or a mixture thereof
may also be present. The optional third carboxylic acid often is a
mono-carboxylic acid having a poly(alkylene oxide) group. Some
exemplary third carboxylic acids have 5 to 30 carbon atoms, 5 to 20
carbon atoms, 5 to 16 carbon atoms, or 5 to 12 carbon atoms.
[0039] Other materials can be added to the feedstock solution of
the continuous hydrothermal reactor. For example, other acids such
as other soluble, mono-carboxylic acids can be added. These
additional acids may modify the surface of the resulting acicular
boehmite nanoparticle. That is, these additional acids may sorb on
the surface of the resulting acicular boehmite nanoparticle. In
some embodiments, an additional mono-carboxylic acid having a
polyalkylene oxide group can be added to the feedstock solution.
The polyalkylene oxide group contains repeating alkylene oxide
units of the general formula --O--R-- where R is an alkylene group
such as, for example, methylene, ethylene and propylene (including
n-propylene and iso-propylene) or a combination thereof. Suitable
poly(alkylene oxide)-containing carboxylic acids usually have at
least five carbon atoms and can be of Formula (II). Some exemplary
poly(alkylene oxide)-containing carboxylic acids have 5 to 30
carbon atoms, 5 to 20 carbon atoms, 5 to 16 carbon atoms, or 5 to
12 carbon atoms. Exemplary poly(alkylene oxide) carboxylic acids
include, but are not limited to,
2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEAA) and
2-(2-methoxyethoxy)acetic acid (MEAA). In other embodiments, the
additional mono-carboxylic acid can be an alpha-hydroxyl acid. The
alpha-hydroxyl acid often has a single carboxyl group and up to 20
carbon atoms. The alpha-hydroxyl acid often contains up to 16
carbon atoms, up to 12 carbon atoms, up to 8 carbon atoms, up to 6
carbon atoms, or up to 4 carbon atoms. Exemplary alpha-hydroxyl
acids include, but are not limited to, lactic acid and glycolic
acid. These modifying acids, if included in the feedstock solution,
are typically present in an amount no greater than 0.2 moles per
mole of aluminum, no greater than 0.1 mole per mole of aluminum. or
not greater than 0.05 moles per mole of aluminum.
[0040] If these additional acids are added to the feedstock, longer
residence times may be needed within the continuous hydrothermal
reactor to produce the acicular boehmite nanoparticles. However,
the use of these additional acids may be desirable if the resulting
acicular boehmite nanoparticles will be subsequently dispersed or
suspended in an organic matrix. The additional acids tend to sorb
on the surface of the boehmite nanoparticles rendering them more
compatible with the organic matrix, with various surface
modification agents, or with both.
[0041] The pH of the feedstock solution is typically no greater
than 6. If the pH is higher than 6, acicular shaped acicular
boehmite nanoparticles typically are not formed during the
hydrolysis and condensation reactions within the continuous
hydrothermal reactor. The pH is often no greater than 5.5 or no
greater than 5. The pH can be in the range of 3 to 6, in the range
of 3 to 5, or close to 4. The pH of the feedstock solution can be
lowered, if necessary, by the addition of a soluble mono-carboxylic
acid.
[0042] The feedstock solution typically does not contain nitrate
ions or halide ions. That is, the feedstock solution is typically
free or substantially free of halide and nitrate ions. As used
herein, the term "substantially free" with reference to halide and
nitrate ions means that these ions are not intentionally added but
may be present as impurities in other components of the feedstock
solution. Any nitrate ions sorbed on the formed acicular boehmite
nanoparticles or remaining when the acicular boehmite nanoparticles
are suspended or dispersed in an organic matrix may result in the
undesirable oxidation of the organic matrix. Halides, on the other
hand, tend to be quite corrosive and can be incompatible with the
organic matrix. If the boehmite is used to prepare a ceramic
material, the presence of halides can be particularly undesirable.
The feedstock solution contains no greater than 10 millimolar, no
greater than 5 millimolar, no greater than 1 millimolar, or no
greater than 0.5 millimolar halide or nitrate. That is, the
concentration of halide or nitrate in the feedstock solution is in
the range of 0 to 10 millimolar, in the range of 0 to 5 millimolar,
in the range of 0 to 1 millimolar, or in the range of 0 to 0.5
millimolar.
[0043] The feedstock solution is passed through a continuous
hydrothermal reactor. Any known design of a continuous hydrothermal
reactor can be used. For example, some suitable continuous
hydrothermal reactors are described in an article by Adschiri et
al., J. Am. Ceram. Soc., 75 (4), 1019-1022 (1992) and in U.S. Pat.
No. 5,453,262 (Dawson et al). In these designs, the portion of the
continuous hydrothermal reactor system that is heated includes a
tube that is straight and that has a surrounding
electrical-resistance heater.
[0044] One exemplary continuous hydrothermal reactor system 100 is
shown schematically in FIG. 1. The feedstock solution 110 is
contained within a feedstock solution tank 115. The feedstock
solution tank is connected with tubing or piping 117 to a pump 120.
Similar tubing or piping can be used to connect other components of
the hydrothermal reactor system. The tubing or piping 117 can be
constructed of any suitable material such as metal, polymer, glass,
or ceramic. In some embodiments, the tubing or piping 117 can be
polyethylene tubing or polypropylene tubing in the portions of the
continuous hydrothermal reactor system 100 that are not heated and
that are not under high pressure. The pump 120 is used to introduce
the feedstock solution 110 into the tubular reactor 130. That is,
the pump 120 is connected to the inlet of the tubular reactor 130.
Any type of pump 120 can be used that is capable of pumping against
the pressure within the tubular reactor 130. The pump can provide a
constant or pulsed flow of the feedstock solution into the tubular
reactor 130.
[0045] As used herein, the term "tubular reactor" refers to the
portion of the continuous hydrothermal reactor system that is
heated (i.e., the heated zone). Although the tubular reactor 130 is
shown in FIG. 1 as a coil of tubing, the tubular reactor can have
any suitable shape. The shape of the tubular reactor is often
selected based on the desired length of the tubular reactor and the
method used to heat the tubular reactor. For example, the tubular
reactor can be straight, U-shaped, or coiled. The interior potion
of the tubular reactor can be empty or can contain baffles, balls,
or other known mixing means.
[0046] As shown in FIG. 1, the tubular reactor 130 is placed in a
heating medium 140 within a heating medium vessel 150. The heating
medium 140 can be, for example, an oil, sand, salt, or the like
that can be heated to a temperature above the hydrolysis and
condensation temperatures of the aluminum-containing precursor of
Formula (I). Suitable oils include, for example, plant oils such as
peanut oil and canola oil. Some plant oils are preferably kept
under nitrogen when heated to prevent or minimize oxidation of the
oils. Other suitable oils include polydimethylsiloxanes such as
those commercially available from Duratherm Extended Fluids
(Lewiston, N.Y.) under the trade designation "DURATHERM S".
Suitable salts include, for example, sodium nitrate, sodium
nitrite, potassium nitrate, or mixtures thereof. The heating medium
vessel 150 can be any suitable container that can hold the heating
medium and withstand the heating temperatures used for the tubular
reactor 130. The heating medium vessel 150 can be heated using any
suitable means. In many embodiments, the heating medium vessel 150
is positioned inside an electrically heated coil. Alternatively,
other types of heaters such as, for example, induction heaters,
microwave heaters, fuel-fired heaters, heating tape, and steam
coils can be used in place of the heating vessel 150, the heating
medium 140, or both.
[0047] The tubular reactor 130 can be made of any material capable
of withstanding the temperatures and pressures used to prepare
acicular boehmite nanoparticles. The tubular reactor 130 preferably
is constructed of a material that can resist dissolution in the
presence of an acidic environment. For example, carboxylic acids
can be present in the feedstock or can be produced as a reaction
byproduct within the continuous hydrothermal reactor system. In
some exemplary embodiments, the tubular reactor is made of
stainless steel, nickel, titanium, carbon-based steel, or the
like.
[0048] In other exemplary embodiments, an interior surface of the
tubular reactor contains a fluorinated polymeric material. This
fluorinated polymeric material can include, for example, a
fluorinated polyolefin. In some embodiments, the fluorinated
polymeric material is polytetrafluoroethylene (PTFE) such as
TEFLON, which is a trade designation of DuPont (Wilmington, Del.).
Some tubular reactors have a fluorinated polymeric hose such as a
PTFE hose within a metal housing such as a braided stainless steel
housing. Surprisingly, the heat transfer is typically sufficient
through the fluorinated polymeric material to convert the
aluminum-containing precursor in the feedstock solution to acicular
boehmite nanoparticles under continuous hydrothermal conditions.
The fluorinated polymeric surface is particularly advantageous for
use with feedstock solutions and/or reaction products that contain
carboxylic acids. These carboxylic acids can leach metals from some
known hydrothermal reactors such as those constructed of stainless
steel.
[0049] The second end of the tubular reactor 130 is usually
connected to a cooling device 160. Any suitable cooling device 160
can be used. In some embodiments, the cooling device 160 is a heat
exchanger that includes a section of tubing or piping with an outer
jacket filled with a cooling medium such as cool water. In other
embodiments, the cooling device 160 includes a coiled section of
tubing or piping that is placed in a vessel that contains cooling
water. In either of these embodiments, the reactor effluent is
passed through the section of tubing and is cooled from the tubular
reactor temperature to a temperature no greater than 100.degree.
C., no greater than 80.degree. C., no greater than 60.degree. C.,
or no greater than 40.degree. C. Other cooling devices that contain
dry ice or refrigeration coils can also be used. After cooling, the
reactor effluent can be discharged into a product collection vessel
180. The tubular reactor effluent is preferably not cooled below
the freezing point prior to being discharged into the product
collection vessel 180.
[0050] The pressure inside the tubular reactor can be at least
partially controlled with a backpressure valve 170, which is
generally positioned between the cooling device 160 and the sample
collection vessel 180. The backpressure valve 170 controls the
pressure at the exit of the continuous hydrothermal reactor system
100 and helps to control the pressure within the tubular reactor
130. The backpressure is often at least 100 pounds per square inch
(0.7 MPa), at least 200 pounds per square inch (1.4 MPa), at least
300 pounds per square inch (2.1 MPa), at least 400 pounds per
square inch (2.8 MPa), at least 500 pounds per square inch (3.5
MPa), at least 600 pounds per square inch (4.2 MPa), or at least
700 pounds per square inch (4.9 MPa). The backpressure should be
high enough to prevent boiling within the tubular reactor 130.
[0051] The dimensions of the tubular reactor 130 can be varied and,
in conjunction with the flow rate of the feedstock solution, can be
selected to provide suitable residence times for the reactants
within the tubular reactor. As used herein, the term "residence
time" refers to the average length of time that the feedstock is
within the heated zone of the continuous hydrothermal reactor
system. That is, the residence time is the average time the
feedstock is within the tubular reactor 130 and is equal to the
tubular reactor volume divided by the flow rate of the feedstock
solution. Any suitable length tubular reactor can be used provided
that the residence time is sufficient to convert the
aluminum-containing precursor to acicular boehmite nanoparticles.
The tubular reactor often has a length of at least 0.5 meter, at
least 1 meter, at least 2 meters, at least 5 meters, at least 10
meters, at least 15 meters, at least 20 meters, at least 30 meters,
at least 40 meters, or at least 50 meters. The length of the
tubular reactor in some embodiments is less than 500 meters, less
than 400 meters, less than 300 meters, less than 200 meters, less
than 100 meters, less than 80 meters, less than 60 meters, less
than 40 meters, or less than 20 meters.
[0052] Tubular reactors with a relatively small inner diameter are
typically preferred. For example, tubular reactors having an inner
diameter no greater than about 3 centimeters are often used because
a relatively fast rate of heating of the feedstock solution can be
achieved with these reactors. Also, the temperature gradient across
the tubular reactor is smaller for reactors with a smaller inner
diameter compared to those with a larger inner diameter. The larger
the inner diameter of the tubular reactor, the more this reactor
undesirably resembles a batch reactor. However, if the inner
diameter of the tubular reactor is too small, there is an increased
likelihood of the reactor becoming plugged or partially plugged
during operation resulting from deposition of material on the walls
of the reactor. The inner diameter of the tubular reactor is often
at least 0.1 centimeters, at least 0.15 centimeters, at least 0.2
centimeters, at least 0.3 centimeters, at least 0.4 centimeters, at
least 0.5 centimeters, or at least 0.6 centimeters. In some
embodiments, the diameter of the tubular reactor is no greater than
3 centimeters, no greater than 2.5 centimeters, no greater than 2
centimeters, no greater than 1.5 centimeters, or no greater than
1.0 centimeters. Some tubular reactors have an inner diameter in
the range of 0.1 to 3.0 centimeters, in the range of 0.2 to 2.5
centimeters, in the range of 0.3 to 2 centimeters, in the range of
0.3 to 1.5 centimeters, or in the range of 0.3 to 1 centimeter.
[0053] Rather than increasing the inner diameter of the tubular
reactor, it may be preferable to use multiple tubular reactors
having a smaller inner diameter arranged in a parallel manner. For
example, rather than increasing the inner diameter of the tubular
reactor to produce a larger amount of acicular boehmite
nanoparticle, multiple tubular reactors having an inner diameter no
greater than about 3 centimeters can be operated in parallel.
[0054] Any suitable flow rate of the feedstock through the tubular
reactor can be used as long as the residence time is sufficiently
long to convert the aluminum-containing precursor to acicular
boehmite nanoparticles. Higher flow rates are desirable for
increasing throughput and minimizing the deposition of materials on
the walls of the tubular reactor. The flow rate is often selected
based on the residence time needed to convert the
aluminum-containing precursor to acicular boehmite nanoparticles. A
higher flow rate can often be used when the length of the tubular
reactor is increased or when both the length and diameter of the
tubular reactor are increased. The flow through the tubular reactor
can be either laminar or turbulent.
[0055] The tubular reactor is held at a temperature that is greater
than the hydrolysis and condensation reaction temperatures of the
aluminum-containing precursor. The temperature is often at least
130.degree. C., at least 140.degree. C., or at least 150.degree. C.
In some embodiments, the aspect ratio of the resulting acicular
boehmite nanoparticle tends to decrease when the reactor
temperature is increased. If the temperature is too high, the
pressure of the tubular reactor may be unacceptably high. The
temperature is typically no greater than 230.degree. C., no greater
then 225.degree. C., or no greater than 220.degree. C. In many
embodiments, the reaction temperature is selected to be in the
range of 130.degree. C. to 230.degree. C., in the range of
140.degree. C. to 220.degree. C., in the range of 140.degree. C. to
200.degree. C., in the range of 150.degree. C. to 200.degree. C.,
or in the range of 150.degree. C. to 180.degree. C.
[0056] The residence time in the tubular reactor can be varied by
altering the length or diameter of the tubular reactor as well as
by altering the flow rate of the feedstock solution. In many
embodiments, the residence time is at least 2 minutes, at least 4
minutes, at least 6 minutes, at least 8 minutes, or at least 10
minutes. The residence time is typically no greater than 90
minutes, no greater than 60 minutes, no greater than 50 minutes, no
greater than 40 minutes, or no greater than 30 minutes. In many
examples, the residence time is in the range of 2 to 90 minutes, in
the range of 2 to 60 minutes, in the range of 5 to 60 minutes, in
the range of 5 to 50 minutes, in the range of 5 to 40 minutes, in
the range of 5 to 30 minutes, in the range of 10 to 30 minutes, or
in the range of 10 to 20 minutes.
[0057] The effluent of the continuous hydrothermal reactor contains
acicular boehmite nanoparticles. The acicular boehmite
nanoparticles are dispersed or suspended in an aqueous-based
solvent. This aqueous-based solvent often contains dissolved
carboxylic acids and/or anions thereof that are present in the
feedstock solution, that are byproducts of the reactions that occur
within the tubular reactors, or both. As used herein, the phrase
"carboxylic acid and/or anions thereof" refers to a carboxylic
acid, an anion of the carboxylic acid (i.e., the carboxylate anion
corresponding to the carboxylic acid), or a mixture thereof. The
effluent often contains (a) a dissolved first carboxylic acid
and/or an anion thereof and (b) a dissolved second carboxylic acid
and/or an anion thereof. The first carboxylic acid is formic acid
or acetic acid. The second carboxylic acid, which is different than
the first carboxylic acid, is acetic acid, propionic acid, butyric
acid, or a mixture thereof. The effluent can also contain an
optional dissolved third carboxylic acid having at least 5 carbon
atoms, an anion of the optional third carboxylic acid, or a mixture
thereof.
[0058] The effluent from the hydrothermal reactor can be clear or
slightly turbid depending on the size of the particles and the
degree of agglomeration. Turbidity increases with an increase in
the average particle size and with an increase in the extent of
agglomeration. As it exits the hydrothermal reactor system, the
effluent is typically fluid (e.g., the viscosity is less then 300
centipoises, less than 200 centipoises, less than 150 centipoises,
or less than 100 centipoises). If the effluent is not treated to
remove various dissolved salts from the effluent, the viscosity can
increase over time and the effluent can become a gel. Depending on
the concentration of the effluent, the gel can form within minutes
or hours. Gels tend to form more quickly from more concentrated
effluents.
[0059] For many applications, removal of at least some of the
aqueous-based solvent from the effluent of the hydrothermal reactor
is desirable. In particular, removal of at least a portion of the
water in the aqueous-based solvent can be desirable. Any suitable
means known in the art can be used to remove at least a portion of
the water. For example, methods such as vaporization, drying, and
solvent exchange can be used. The removal of at least some of the
water can be accompanied by the removal of at least a portion of
the dissolved carboxylic acids and/or anions thereof. For example,
the removal of at least some of the water in the effluent may be
accompanied by the removal of at least a portion of the first
carboxylic acid and/or anion thereof plus the removal of at least a
portion of the second carboxylic acid and/or anion thereof.
[0060] In some embodiments, at least a portion of the water in the
effluent from the continuous hydrothermal reactor can be removed by
drying the effluent. The drying process can also result in the
vaporization of at least some of the carboxylic acids such as those
having no more than 4 carbon atoms. Any suitable drying method can
be used such as spray drying, gap drying, or oven drying. For
example, the effluent can be dried in a conventional oven at a
temperature of at least 80.degree. C., at least 90.degree. C., at
least 100.degree. C., at least 110.degree. C., or at least
120.degree. C. The drying time is often greater than 30 minutes,
greater than 1 hour, greater than 2 hours, or greater than 3
hours.
[0061] In still other embodiments, at least a portion of the water
in the effluent of the continuous hydrothermal reactor can be
removed using a solvent exchange method. An organic solvent with a
higher boiling point than water can be added to the effluent.
Examples of organic solvents that are suitable for use in a solvent
exchange method include, but are not limited to,
1-methoxy-2-propanol and N-methylpyrrolidone. The mixture
containing the effluent plus the organic solvent can be treated to
remove the water using methods such as, for example, distillation,
rotary evaporation, or oven drying. Depending on the conditions, at
least a portion of the dissolved carboxylic acids and/or anions
thereof also may be removed by the solvent exchange method.
[0062] In some applications, it may be desirable to remove at least
a portion of the dissolved carboxylic acids and/or anions thereof
in the effluent of the continuous hydrothermal reactor. Removal of
at least a portion of the dissolved carboxylic acids and/or anions
thereof may be desirable to minimize formation of a gel or when the
acicular boehmite nanoparticles will be suspended or dispersed in
an organic matrix. Any known method can be used to remove the
dissolved carboxylic acids and/or anions thereof. For example,
these species can be removed using dialysis, diafiltration, or an
anion exchange resin.
[0063] If dialysis is used to remove at least a portion of the
dissolved carboxylic acids and/or anions thereof in the effluent of
the hydrothermal treatment, a sample of the effluent can be
positioned within a membrane bag that is closed and then placed
within a water bath. A membrane bag is typically selected that
allows diffusion of the carboxylic acids and/or anions thereof but
does not allow diffusion of the acicular boehmite nanoparticles out
of the membrane bag. The carboxylic acid and/or carboxylate anions
diffuse out of the sample within the membrane bag. That is, these
species will diffuse out of the effluent within the membrane bag
into the water bath to equalize the concentration within the
membrane bag to the concentration in the water bath. The water in
the bath is typically replaced several times to lower the
concentration of species within the bag.
[0064] For diafiltration, a permeable membrane is used to filter
the sample. The acicular boehmite nanoparticles can be retained on
the filter if the pore size of the filter is appropriately chosen.
The dissolved carboxylic acids and/or anions thereof pass through
the filter. Any liquid that passes through the filter is replaced
with fresh water. In a discontinuous diafiltration process, the
sample is often diluted to a pre-determined volume and then
concentrated back to the original volume by ultrafiltration. The
dilution and concentration steps are repeated one or more times
until the carboxylic acid and/or anions thereof are removed or
lowered to an acceptable concentration level. In a continuous
diafiltration process, which is often referred to as a constant
volume diafiltration process, fresh water is added at the same rate
that liquid is removed through filtration. The dissolved carboxylic
acid and/or anions thereof are in the liquid that is removed.
[0065] At least a portion of the dissolved carboxylic acid and/or
anions thereof in the effluent of the continuous hydrothermal
reactor also can be removed using an anion exchange resin in a
hydroxyl form. By adjusting the pH of the effluent, the carboxylic
acids can be converted to the basic form (i.e., carboxylate anion).
At least some of the carboxylate anions can replace some of the
hydroxyl ions on the anion exchange resin. The pH adjusted effluent
can be passed through a column containing the anion exchange resin
or through a filtration medium containing the anion exchange resin.
Alternatively, the anion exchange resin can be mixed with the
effluent of the continuous hydrothermal reactor. After ion
exchange, the anion exchange resin can be removed by filtration.
The size of the anion exchange resin is selected so that it can be
easily filtered from the treated effluent. For example, the size of
the anion exchange resin is often no greater than 200 mesh, no
greater than 100 mesh, or no greater than 50 mesh.
[0066] The acicular boehmite nanoparticles in the effluent from the
continuous hydrothermal reactor usually contain sorbed carboxylic
acids, salts of the carboxylic acids, or mixtures thereof (i.e.,
sorbed modifiers). These sorbed carboxylic acids and/or anions
thereof typically are not removed by the treatments used to remove
the dissolved carboxylic acid and/or anions thereof in the
effluent. Although it may be desirable to remove the carboxylic
acids and/or anions thereof that are dissolved in the effluent of
the continuous hydrothermal reactor, it may be advantageous to have
these same moieties sorbed on the surface of the acicular boehmite
nanoparticle. These sorbed carboxylic acids and/or anions thereof
can function as surface modifiers that can enhance compatibility of
the acicular boehmite nanoparticles with various organic matrix
materials.
[0067] The sorbed modifiers on a surface of the acicular boehmite
nanoparticle include (a) a first carboxylic acid and/or anion
thereof and (b) a second carboxylic acid and/or anion thereof. The
first carboxylic acid is selected from formic acid or acetic acid.
The second carboxylic acid, which is different than the first
carboxylic acid, is selected from acetic acid, formic acid,
propionic acid, butyric acid, or a mixture thereof. In some
embodiments, the first carboxylic acid is formic acid and the
second carboxylic acid is acetic acid, propionic acid, or mixtures
thereof. There can be an optional third carboxylic acid and/or
anion thereof having at least five carbon atoms sorbed on the
surface of the acicular boehmite nanoparticle. The optional third
carboxylic acid and/or anion thereof often has 5 to 30 carbon atoms
and has a poly(alkylene oxide) group.
[0068] The acicular boehmite nanoparticles often contain at least
0.5 weight percent carboxylic acids and/or anions thereof sorbed on
the surface. For example, the acicular boehmite nanoparticle can
contain at least 1.0 weight percent, at least 1.5 weight percent,
at least 2 weight percent, at least 3 weight percent, at least 4
weight percent, or at least 5 weight percent carboxylic acids or
anions thereof based on the weight of the acicular boehmite
nanoparticle.
[0069] The boehmite prepared within the continuous hydrothermal
reactor system is an acicular nanoparticle. The average aspect
ratio is at least 3:1. As used herein, the term "aspect ratio"
refers to the ratio of the length of the boehmite nanoparticle to
the width of the boehmite nanoparticle. In some embodiments, the
average aspect ratio is at least 4:1, at least 5:1, at least 6:1,
at least 8:1, or at least 10:1. A large aspect ratio is desirable
for many applications because fewer acicular boehmite nanoparticles
need to be added to produce the desired effect. For example, the
amount of the acicular boehmite nanoparticles needed to produce a
composite material with a desired tensile strength can be lowered
by increasing the aspect ratio of the acicular boehmite
nanoparticles. The dimensions of the acicular boehmite nanoparticle
can be measured, for example, by measuring at least 50 particles on
a transmission electron micrograph.
[0070] The acicular boehmite nanoparticles usually have an average
length no greater than 1000 nanometers, no greater than 500
nanometers, no greater than 400 nanometers, no greater than 300
nanometers, no greater than 200 nanometers, or no greater than 100
nanometers. The average length is typically at least 5 nanometers,
at least 10 nanometers, at least 20 nanometers, at least 30
nanometers, at least 40 nanometers, or at least 50 nanometers. For
example, the average length can be in the range of 5 to 500
nanometers, in the range of 20 to 500 nanometers, in the range of
10 to 400 nanometers, in the range of 20 to 400 nanometers, in the
range of 10 to 300 nanometers, in the range of 10 to 200
nanometers, or in the range of 10 to 100 nanometers.
[0071] The average particle width is typically no greater than 20
nanometers, no greater than 15 nanometers, no greater than 12
nanometers, no greater than 10 nanometers, no greater than 8
nanometers, no greater than 6 nanometers, or no greater than 5
nanometers. The average width, for example, can be in the range of
1 to 20 nanometers, in the range of 1 to 15 nanometers, in the
range of 1 to 10 nanometers, or in the range of 2 to 10
nanometers.
[0072] The acicular boehmite nanoparticles typically are
crystalline as determined using x-ray diffraction. The acicular
boehmite nanoparticles are often substantially non-associated or
can be dispersed to be substantially non-associated. As used
herein, the term "non-associated" means that the particles are
substantially free of aggregation and/or agglomeration. Aggregation
refers to a strong association between primary particles such as a
chemical bond. Agglomeration refers to a weaker association between
primary particles such as polar attraction. The breakdown of
agglomerates into smaller particles such as the primary particles
is less difficult than the breakdown of aggregates.
[0073] In yet another aspect, a composite material is provided that
includes an organic matrix and acicular boehmite nanoparticles
dispersed or suspended in the organic matrix. Various sorbed
modifiers are on a surface of the acicular boehmite nanoparticle.
The sorbed modifiers include (a) a first carboxylic acid, an anion
of the first carboxylic acid, or a mixture thereof and (b) a second
carboxylic acid, an anion of the second carboxylic acid, or a
mixture thereof. The first carboxylic acid is selected from formic
acid or acetic acid. The second carboxylic acid, which is different
than the first carboxylic acid, is selected from acetic acid,
formic acid, propionic acid, butyric acid, or a mixture thereof.
There can be an optional third carboxylic acid and/or anion thereof
having at least five carbon atoms sorbed on the surface of the
acicular boehmite nanoparticle. The optional third carboxylic acid
and/or anion thereof often has 5 to 30 carbon atoms and has a
poly(alkylene oxide) group.
[0074] The effluent from the hydrothermal reactor contains acicular
nanoparticles that have sorbed carboxylic acids. In some
applications, the acicular boehmite nanoparticles are compatible
with the organic matrix without any further surface modification.
In other applications, however, the acicular boehmite nanoparticle
is further treated with an additional surface modification agent to
further improve compatibility with the organic matrix material.
[0075] Surface modification agents may be represented by the
formula A-B where the A group is capable of attaching to the
surface of an acicular boehmite nanoparticle and B is a
compatibility group. Group A can be attached to the surface by
adsorption, formation of an ionic bond, formation of a covalent
bond, or a combination thereof. Group B can be reactive or
non-reactive and often tends to impart characteristics to the
acicular boehmite nanoparticles that are compatible (i.e.,
miscible) with an organic solvent, with an organic matrix material,
or both. For example, if the solvent is non-polar, group B is
typically selected to be non-polar as well. Suitable B groups
include linear or branched hydrocarbons that are aromatic,
aliphatic, or both aromatic and aliphatic. The surface modifying
agents include, but are not limited to, carboxylic acids and/or
anions thereof, sulfonic acids and/or anions thereof, phosphoric
acids and/or anions thereof, phosphonic acids and/or anions
thereof, silanes, amines, and alcohols.
[0076] In some embodiments, the surface modification agent is a
carboxylic acid and/or anion thereof and the compatibility B group
can impart a polar character to the acicular boehmite
nanoparticles. For example, the surface modification agent can be a
carboxylic acid and/or anion thereof having a polyalkylene oxide
group. Representative examples include
2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEAA),
2-(2-methoxyethoxy)acetic acid (MEAA), and mono(polyethylene
glycol)succinate.
[0077] In other embodiments, the surface modification agent is a
carboxylic acid and/or anion thereof and the compatibility B group
can impart a non-polar character to the acicular boehmite
nanoparticles. For example, the surface modification agent can be a
carboxylic acid and/or anion thereof having a linear or branched
aromatic group or aliphatic hydrocarbon group. Representative
examples of include octanoic acid, dodecanoic acid, stearic acid,
oleic acid, and combinations thereof.
[0078] In still other embodiments, the surface modification agent
is a carboxylic acid and/or anion thereof and the compatibility B
group can be reactive with a polymerizable organic matrix (e.g.,
the B group contains a polymerizable group). Reactive carboxylic
acid surface modifying agents (e.g., carboxylic acids with
polymerizable groups) include, for example, acrylic acid,
methacrylic acid, beta-carboxyethyl acrylate,
mono-2-(methacryloxyethyl)succinate, and combinations thereof. A
useful surface modification agent that can impart both polar
character and reactivity to the acicular boehmite nanoparticles is
mono(methacryloxypolyethyleneglycol) succinate. This material may
be particularly suitable for addition to radiation curable acrylate
and/or methacrylate organic matrix materials.
[0079] Exemplary silane surface modification agents include, but
are not limited to, alkyltrialkoxysilanes such as
n-octyltrimethoxysilane, n-octyltriethoxysilane,
isooctyltrimethoxysilane, dodecyltrimethoxysilane,
octadecyltrimethoxysilane, propyltrimethoxysilane, and
hexyltrimethoxysilane; methacryloxyalkyltrialkoxysilanes or
acryloxyalkyltrialkoxysilanes such as
3-methacryloxypropyltrimethoxysilane,
3-acryloxypropyltrimethoxysilane, and
3-(methacryloxy)propyltriethoxysilane;
methacryloxyalkylalkyldialkoxysilanes or
acryloxyalkylalkyldialkoxysilanes such as
3-(methacryloxy)propylmethyldimethoxysilane, and
3-(acryloxypropyl)methyldimethoxysilane;
methacryloxyalkyldialkylalkoxysilanes or
acyrloxyalkyldialkylalkoxysilanes such as
3-(methacryloxy)propyldimethylethoxysilane;
mercaptoalkyltrialkoxylsilanes such as
3-mercaptopropyltrimethoxysilane; aryltrialkoxysilanes such as
styrylethyltrimethoxysilane, phenyltrimethoxysilane,
phenyltriethoxysilane, and p-tolyltriethoxysilane; vinyl silanes
such as vinylmethyldiacetoxysilane, vinyldimethylethoxysilane,
vinylmethyldiethoxysilane, vinyltrimethoxysilane,
vinyltriethoxysilane, vinyltriacetoxysilane,
vinyltriisopropoxysilane, vinyltrimethoxysilane,
vinyltriphenoxysilane, vinyltri-t-butoxysilane,
vinyltris(isobutoxy)silane, vinyltriisopropenoxysilane, and
vinyltris(2-methoxyethoxy)silane; 3-glycidoxypropyltrialkoxysilane
such as glycidoxypropyltrimethoxysilane; polyether silanes such as
N-(3-triethoxysilylpropyl)methoxyethoxyethoxyethyl carbamate
(PEG3TES), N-(3-triethoxysilylpropyl)methoxyethoxyethoxyethyl
carbamate (PEG2TES), and SILQUEST A-1230; and combinations
thereof.
[0080] Whether or not an additional surface modification agent is
added to the surface of the acicular boehmite nanoparticles, at
least a portion of the water in the effluent of the hydrothermal
reactor is often removed prior to mixing the acicular boehmite
nanoparticles with an organic matrix. In some examples, the
effluent from the continuous hydrothermal reactor can be dried at a
temperature suitable for removing water plus at least a portion of
the dissolved carboxylic acid and/or anions thereof. If no
additional surface modification agent is added, the dried acicular
boehmite nanoparticle can be suspended or dispersed in an organic
matrix. When the dried acicular boehmite nanoparticle is mixed with
the organic matrix, an optional organic solvent can be present that
may be subsequently removed.
[0081] If an additional surface modification agent is added, the
dried acicular boehmite nanoparticle can be mixed initially with
the surface modification agent in an optional organic solvent.
After surface treatment, the surface modified acicular boehmite
nanoparticle can be mixed with an organic matrix. The optional
organic solvent can be removed before or after addition of the
organic matrix. Alternatively, if an additional surface
modification agent is added, the dried acicular boehmite
nanoparticle can be mixed with both the organic matrix and the
surface modification agent in the presence of an optional organic
solvent. The optional organic solvent can be removed after surface
modification.
[0082] In another example, at least a portion of the water can be
removed from the effluent of the continuous hydrothermal reactor by
a solvent exchange process. An organic solvent having a higher
boiling point than water is added to the effluent. The water can be
removed by a method such as, for example, distillation, rotary
evaporation, oven drying, or the like. Depending on the conditions
used for removing the water, at least a portion of the dissolved
carboxylic acid and/or anion thereof also can be removed. If no
additional surface modification agent is added, the organic matrix
can be added to the treated effluent (i.e., the organic matrix is
added to the acicular boehmite nanoparticle suspended in the
organic solvent used in the solvent exchange process).
[0083] If an additional surface modification agent is added, the
additional surface modification agent can be added either before or
after the solvent exchange process. The surface modification agent
can be selected to facilitate the extraction of the acicular
boehmite nanoparticles in to the organic solvent used in the
solvent exchange process. The organic matrix can be added after the
solvent exchange process. Alternatively, the organic matrix,
organic solvent, and the additional surface modification agent can
be added at the same time. The organic solvent used in the solvent
exchange process can often be removed after addition of the organic
matrix using a method such as distillation, rotary evaporation,
oven drying, or the like.
[0084] In some applications, the organic solvent, the organic
matrix, and a surface modification agent are all mixed with the
effluent of the hydrothermal reactor. The water and organic solvent
are then removed by distillation. At least some of the dissolved
carboxylic acid and/or anions thereof in the effluent are also
removed during distillation.
[0085] In yet another example, the dissolved carboxylic acid and/or
anion thereof in the effluent from the continuous hydrothermal
reactor can be removed by a process such as dialysis or ion
exchange. If no additional surface modification agent is added, an
organic matrix can be added either before or after removal of most
of the water from the treated effluent. If the organic matrix is
added before removal of most of the water and the boiling point of
the organic matrix is greater than the boiling point of water, the
water can be removed using a method such as distillation, rotary
evaporation, or oven drying. Alternatively, the pH of the treated
effluent can be adjusted to precipitate the acicular boehmite
nanoparticle. The precipitated acicular boehmite nanoparticle can
be collected by filtration or centrifugation. Any remaining water
can be removed either before or after mixing the filtered or
centrifuged acicular boehmite nanoparticle with an organic
matrix.
[0086] If an additional surface modification agent is used, this
additional surface modification agent can be added directly to the
effluent treated using ion exchange or dialysis or to untreated
effluent. Optionally, a polar co-solvent may be added to increase
the solubility of the surface modification agent in the aqueous
phase. Suitable polar co-solvents include water-miscible organic
compounds such as, for example, 1-methoxy-2-propanol, ethanol,
isopropanol, ethylene glycol, N,N-dimethylacetamide, N-methyl
pyrrolidone, or the like. The organic matrix can be added either
before or after removal of most of the water and optional polar
co-solvents. The water and optional polar co-solvent can be
removed, for example, by distillation, rotary evaporation, or oven
drying if the organic matrix has a higher boiling point. The water
and optional polar co-solvent can also be removed by precipitation
of the surface modified acicular boehmite nanoparticle by adjusting
the pH. Alternatively, the surface modification agent can change
the polarity of the acicular boehmite nanoparticles resulting in
the precipitation of the surface modified acicular boehmite
nanoparticles. The precipitated acicular boehmite nanoparticle can
be separated from the liquid phase by filtration or centrifugation.
Any remaining water and optional co-solvent can be removed either
before or after mixing the filtered or centrifuged acicular
boehmite nanoparticle with an organic matrix.
[0087] Alternatively, if an additional surface modification agent
is added, both the surface modification agent and the organic
matrix can be added directly to untreated effluent or effluent
treated using ion exchange or dialysis. An optional polar
co-solvent can be added. After addition of the organic matrix, the
water and optional polar co-solvent can be removed, for example, by
distillation, rotary evaporation, oven drying, or the like. As
another alternative, the treated effluent can be dried before
combination with an additional surface modification agent, organic
matrix, or both. In this alternative, the surface modification
agent can be added with an optional organic solvent either before
or concurrently with the addition of the organic matrix.
[0088] The surface modification reactions can occur at room
temperature (e.g., 20.degree. C. to 25.degree. C.) or at an
elevated temperature (e.g., up to about 95.degree. C.). When the
surface modification agents are acids such as carboxylic acids, the
acicular boehmite nanoparticles typically can be surface-modified
at room temperature. When the surface modification agents are
silanes, the acicular boehmite nanoparticles are typically surface
modified at elevated temperatures.
[0089] The organic matrix typically includes a polymeric material
or a precursor to a polymeric material such as a monomer or a
oligomer having a polymerizable group. Any suitable technique can
be used to combine the acicular boehmite nanoparticles with the
organic matrix. For example, if the organic matrix is a precursor
to a polymeric material, the acicular boehmite nanoparticles can be
added prior to the polymerization reaction. If the polymeric
material is a thermoplastic, the polymeric material and the
acicular boehmite nanoparticles can be combined using a process
such as extrusion, milling or Brabender mixing. The composite
material containing a precursor of a polymeric material is often
shaped or coated before polymerization.
[0090] Representative examples of monomers include, but are not
limited to, (meth)acrylates, styrenes, epoxies, and the like.
Representative examples of reactive oligomers include, but are not
limited to, (meth)acrylated polyesters, (meth)acrylated
polyurethanes, or acrylics. Representative examples of polymeric
material include, but are not limited to, polyolefins, polyesters,
polyurethanes, poly(meth)acrylates, polystyrenes, polycarbonates,
and polyimides.
[0091] One exemplary process for forming a composite material
includes concentrating the effluent from the hydrothermal reactor
to about 40 percent solids or more using a method such as
distillation or rotary evaporation. A co-solvent and surface
modification agent can be added to the concentrate. After addition
of the organic matrix, the co-solvent, and water are removed. At
least a portion of the dissolved carboxylic acid and/or anion
thereof can be removed during the concentration step or after
surface modification.
[0092] The addition of the acicular boehmite nanoparticles to an
organic matrix such as a polymeric material can be advantageous.
For example, the acicular boehmite nanoparticles can be added to
increase the tensile strength of a polymeric material or can be
added as a thickener to an organic matrix. Because the
nanoparticles can be smaller than the wavelengths of visible light,
their presence in an organic matrix often cannot be detected with
the unaided eye. That is, the tensile strength or thickness of an
organic matrix can be increased without affecting the appearance of
the organic matrix. For example, the acicular boehmite
nanoparticles can be suspended or dispersed in an organic matrix
for applications where a high optical transmission is desired.
EXAMPLES
Test Methods
[0093] High-Resolution Thermogravimetric Analysis The acicular
boehmite nanoparticle samples were analyzed using the TA
Instruments 2950 Thermogravimetric Analyzer (TGA), which is
commercially available from TA Instruments (New Castle, Del.). Each
sample was placed on a weighed platinum thermogravimetric analysis
pan. A linear heating rate of 10.degree. C./min was applied with a
resolution setting of 4.0. Under these conditions, the instrument
heated the sample until weight loss was detected. The temperature
was held constant until the weight loss diminished and then the
temperature was increased again. The samples were subjected to a
heating profile ranging from room temperature to 1000.degree. C. in
a nitrogen atmosphere. The TGA data analyses include the weight
loss step analysis results, and the residual weight after the test
cycle was complete.
Headspace GC/MS Analysis Method
[0094] Roughly 0.1 grams of each acicular boehmite nanoparticle
sample was sealed in a separate 20 milliliter headspace vial. The
vials were heated for 60 minutes at 150.degree. C. in the HP7694
Headspace Sampler, which is commercially available from Agilent
Technologies Inc. (Santa Clara, Calif.). Helium (1 mL heated at
160.degree. C.) was used to extract an aliquot of the headspace gas
and convey it via a transfer line heated at 180.degree. C. into the
HP6890 Gas Chromatograph (GC) fitted with a ZEBRON ZB-5 ms column.
This gas chromatograph is commercially available from Agilent
Technologies Inc. (Santa Clara, Calif.). The column has dimensions
of 30 meter by 0.32 millimeter by 1 micrometer and is commercially
available from Phenomenex (Torrance, Calif.).
[0095] The GC column was heated from -20.degree. C. to 150.degree.
C. at 10.degree. C./min and from 150.degree. C. to 310.degree. C.
at 20.degree. C./min. The GC column was held at 310.degree. C. for
5 minutes to ensure that the entire sample had been eluted. Helium
was passed through the column with a flow rate of 2.0 mL/min. The
separated components passed into the HP5973 mass selective detector
where they were subjected to electron bombardment at 70 eV. The
mass selective detector is commercially available from Agilent
Technologies Inc. (Santa Clara, Calif.). A full scan unit
resolution mass spectra from 29 to 500 m/z was detected and
recorded.
X-ray Scattering (XRD)
[0096] Samples were placed on zero background specimen holders
composed of single crystal quartz. Reflection geometry data were
collected in the form of a survey scan by use of a vertical
diffractometer, copper K.sub..alpha. radiation, and proportional
detector registry of the scattered radiation. The diffractometer,
which is commercially available from PANalytical (Westborough,
Mass.), was fitted with variable incident beam slits, fixed
diffracted beam slits, and a graphite diffracted beam
monochromator. The survey scan was conducted from 5 to 80 degrees
(2.theta.) using a 0.04 degree step size and 24 second dwell time.
The x-ray generator settings of 45 kV and 35 mA were used.
[0097] The observed diffraction peaks were subjected to profile
fitting using a Pearson VII peak shape model, a cubic spline
background correction model, and analysis using JADE version 7.5
X-ray diffraction software from MDI (Materials Data Inc. of
Livermore Calif.). The apparent crystallite size (D) was determined
using the Scherrer equation.
Crystallite Size (D)=K.lamda./.beta.(cos .theta.)
In the Scherrer equation, K is the shape factor (here 0.9), .lamda.
is the wavelength of the x-ray radiation (here 1.540598 .ANG.),
.beta. is the calculated peak width after correction for
instrumental broadening (in radians), and .theta. equals half the
peak position (scattering angle). .beta. is equal to [calculated
peak FWHM--instrumental breadth] (converted to radians) where FWHM
is full width at half maximum.
[0098] The boehmite examples typically had a (020) peak that had a
higher angle shoulder with the main peak and shoulder shifted to a
lower and a higher angle relative to the expected position of the
(020). Contrary to expectations based on the appearance of the
(020), this splitting was not observed for the (080) peak. The
(120) peak and the (031) peak with maxima at 28.2 and 38.3 degrees
(20) respectively were used for evaluation of crystallite size.
Transmission Electron Microscopy
[0099] Samples for transmission electron microscopy were prepared
on 400 mesh copper grids with a carbon/formvar coating from which
the formvar had been removed via an acetone/chloroform/acetone
wash. Approximately 1 microliter of the sample was dilusted to 3 mL
with high resistance deionized water. The mixture was hand-shaken
for several seconds to assure homogenization. One drop of the
prepared mixture was placed upon its respective copper grid for
about one minute to allow migration of the nanoparticles to the
coated grid surface. The fluid was then wicked away at the edge of
each grid with a tissue commercially available under the trade
designation KIM WIPE. The grid plus nanoparticles were allowed to
air dry for thirty minutes.
[0100] The transmission electron microscope was a Hitachi 9000,
which is commercially available from Hitachi High Technologies
Corporation (Tokyo, Japan), operating at 300 KeV acceleration
potential. The instrument magnification was 20 KX. The nanoparticle
images were collected using a Gatan ULTRASCAN 894 ccd camera (Gatan
Inc. Pleasanton, Calif.) via DigitalMicrograph.TM. software.
Calibration of the images is based upon TEM calibration standard
MAG*I*CAL.TM. made by Norrox Scientific, Ontario, Canada. The
images had a calibrated marker bar. Measurements were made by using
DigitalMicrograph.TM. software and plug in "LabelLength" and then
imported into Microsoft Excel (Microsoft Corporation Redmond,
Wash.) to graph and calculate. Nanoparticle image domains were
visually identified and particle shapes were manually described on
each respective image. Frequent contact among nanoparticles and
lack of contrast with image background precluded automatic image
analysis. That is, the particles for analysis had to be manually
identified for measurement. At least 100 particles were measured.
The geometrical properties of the particles and the associated
standard deviations were calculated.
Continuous Hydrothermal Reactor
[0101] The continuous hydrothermal reactor is shown schematically
in FIG. 1. The feedstock was placed in a glass vessel positioned
several feet higher than the inlet valve of the LEWA ECODOS
diaphragm pump, which is commercially available from LEWA GmbH
(Stuttgart, Germany). The glass vessel had a stock cock that could
be opened to allow the feedstock to exit the glass vessel.
Polyethylene tubing connected the glass vessel to the inlet of the
diaphragm pump. The reactor portion was 50 feet of 0.25 inch ID
Teflon hose with a braided stainless steel exterior which is
immersed in an electrically heated peanut oil bath. The Teflon hose
was obtained from Saint-Gobain Performance Plastics (Bridgewater,
N.J.). The product of the reactor was then cooled by flowing
through 10 feet of 0.25'' OD stainless steel tubing in an ice water
bath. The backpressure for the system is provided by a backpressure
regulator, which is commercially available from Tescom (Elk River,
Minn.). Another piece of polyethylene tubing was used to transport
the product to a suitable collection vessel. The reactant flow rate
was checked periodically using a graduated cylinder and a
stopwatch. The flow was adjusted by changing the length of the pump
stroke. The peanut oil temperature was measured using a
thermocouple which provided feedback to a computer control
algorithm for the autoclave heating elements. The peanut oil was
stirred by a propeller mixer powered by an air motor.
Preparatory Examples 1 to 5
[0102] Aluminum-containing precursors were prepared by digesting
powdered aluminum in a mixture of various carboxylic acid mixtures
and water. The spherical aluminum powder was purchased from
Aldrich, Milwaukee, Wis. Glacial acetic acid (99.5% acid) was
purchased from EMD Chemicals, Darmstadt, Germany, formic acid (97%
acid) was purchased from Alfa Aesar, Ward Hill, Mass., and
propionic acid (99%) was purchased from Avocado Research Chemicals
Ltd, Shore Road, Heysham, Lancashire, UK.
[0103] The compositions of the digestion mixtures are summarized in
Table 1.
TABLE-US-00001 TABLE 1 Preparation of the Aluminum-containing
precursor Aluminum Pro- Total Preparatory Powder Formic Acetic
pionic Water Weight Example (g) Acid (g) Acid (g) Acid (g) (g) (g)
1 27.0 19.0 48.2 0.0 405.8 500 2 27.0 28.5 36.2 0.0 408.3 500 3
27.0 38.0 24.2 0.0 410.9 500 4 27.0 47.4 12.2 0.0 413.5 500 5 27.0
28.5 0.0 44.8 399.7 500
[0104] The components of each digestion mixture were combined in a
1000 ml round bottom flask equipped with a reflux condenser, a
magnetic stirrer, and a heating mantle. After heating each mixture
was heated to about 80.degree. C., an exothermic reaction
commenced. The heat released from the reaction increased the
temperature above 80.degree. C. but below 100.degree. C. After
about an hour, the temperature was about 80.degree. C. At this
point the temperature set point for the heating mantle was raised
to about 100.degree. C. The temperature remained at 100.degree. C.
for 10 to 16 hours or until no more hydrogen gas was observed
escaping from the reactor vent glycerin trap. The heating mantle
was turned off and the solution was allowed to cool to room
temperature. The solution was then vacuum filtered through a first
filter (Whatman Filter No. 50 from Whatman International Ltd.,
Maidstone, England) and then filtered through a second filter
(Whatman Filter No. 54 from Whatman International Ltd.). The
resulting product had an aluminum content of about 5.4 weight
percent based aluminum based on the weight of the total digestion
mixture.
Examples 1 to 6
[0105] Preparatory Examples 1 to 5 were each diluted with 500 mL
deionized water and then passed through the continuous hydrothermal
reactor. The temperature of the reactor portion was controlled at
170.degree. C. The flow rates used were either 10 mL/minute for a
48 minute residence time or 20 mL/minute for a 24 minute residence
time within the heated reactor portion.
[0106] Most of the examples (Examples 1, 2, 4, 5, 6) were dried at
70.degree. C. in a horizontal air flow batch oven. The effluent
from the continuous hydrothermal reactor for each example was
poured into PYREX pans (Corning Inc. Life Sciences, Lowell, Mass.)
to a depth of approximately 6 millimeters. The pan was placed into
the oven where it remained overnight. The dried material was a
translucent brittle film that was easily removed with a stainless
steel laboratory spatula from the glass pan and placed into a clean
glass jar.
[0107] Example 3 was dialyzed. The effluent from the continuous
hydrothermal reactor was poured into a SPECTRAPOR membrane, which
is commercially available from Spectrum Labs (Rancho Dominguez,
Calif.), with a 6 to 8000 molecular weight cut off. The membrane
was closed at the bottom with an overhand knot. The top of the
membrane was subsequently tied off with an overhand knot and the
tube of material was placed in a one gallon jar filled with
deionized water. The water in the jar was changed every working day
for two weeks. A sample of this material was dried for subsequent
testing in the same manner as the rest of the samples as detailed
above.
TABLE-US-00002 TABLE 2 Preparation of Acicular boehmite
nanoparticle Preparatory Flow rate Example Example (mL/min)
Post-treatment 1 1 10 Dried 2 2 20 Dried 3 2 10 Dialysis, then
dried 4 3 10 Dried 5 4 10 Dried 6 5 10 Dried
[0108] Table 3 summarizes the results from the thermogravimetric
analysis (TGA), x-ray diffraction (XRD), and transmission electron
microscopy (TEM) for Example 1 to 6. The TGA Weight Loss, which
corresponds to the temperature where any residual carboxylic acid
might be removed, is equal to the percentage of the initial weight
lost between 47.degree. C. and 111.degree. C. The Crystallite Size
is determined using XRD. Average particle length, average particle
width, and aspect ratio were determined by measurement of at least
50 particles from a transmission electron micrograph of each
example; the results are summarized in Table 4. Table 5 summarizes
the gas chromatographic/mass spectroscopic (GC/MS) headspace
analysis of Examples 1 to 6. FIG. 2 is the transmission electron
micrograph for Example 6.
TABLE-US-00003 TABLE 3 TGA and XRD of Examples 1 to 6 TGA Weight
Loss TGA Residue XRD Crystallite Size Example (%) (%) (nm) 1 9.60
71.00 4.7 2 5.24 72.06 3.1 3 4.64 72.48 3.4 4 4.60 70.80 3.3 5
11.90 63.90 3.5 6 6.94 68.05 3.9
TABLE-US-00004 TABLE 4 TEM Analysis of Examples 1 to 6 Major
Standard Minor Standard Ex- Axis Deviation Axis Deviation Aspect
Standard ample (nm) (nm) (nm) (nm) Ratio Deviation 1 74.1 33.3 7.7
2.5 10.2 4.8 2 58.9 28.9 8.4 3.4 7.9 4 3 76.6 23.7 14.7 3.7 5.4 1.6
4 73.7 22.7 15.5 3.2 4.9 1.4 5 73.5 37.0 5.7 1.9 14.0 8.2 6 88.5
39.0 4.2 1.6 22.4 11.2
TABLE-US-00005 TABLE 5 Headspace Analysis of Examples 1 to 6 Water
Formic acid Acetic acid Propionic acid Example (% area) (% area) (%
area) (% area) 1 79.90 10.98 9.08 2 66.54 18.97 12.89 3 99.63 0.29
0.08 4 72.44 13.62 13.70 5 58.58 26.33 13.90 6 49.08 35.34 0.92
14.26
Example 7
[0109] The acicular boehmite can be modified to facilitate use in
an organic matrix. The dried acicular boehmite nanoparticle of
Example 2 (1.75 grams) can be dispersed in deionized water (48.25
grams) at room temperature in one hour by mixing with a magnetic
stirrer. With continued stirring, 1-methoxy-2-propanol (92.4 grams)
from Alfa Aesar (Ward Hill, Mass.) can be added to the mixture.
Then, 3-trimethoxysilylpropylmethacrylate (1.3 grams) from Alfa
Aesar can be added to the mixture. This mixture can be heated in a
water bath with magnetic stirring at 80.degree. C. for four hours.
After this, the mixture can be stripped under vacuum using a rotary
evaporator (Buchi Labortechnik AG, Flawil, Switzerland) until the
concentration becomes thick. The percent solids is often about 18
weight percent. Then, trimethylolpropane triacrylate (27 grams)
from Alfa Aesar can be added. The mixture can then be stripped
under vacuum for three days at 80.degree. C. in the rotary
evaporator to remove 1-methoxy-2-propanol from the mixture. The
final mixture appears more viscous than the neat trimethylolpropane
triacrylate.
Example 8
[0110] The aluminum-containing precursor for Example 8 was prepared
by digesting 27 grams of aluminum powder (Aldrich Chemical Company,
Milwaukee, Wis.) in a solution containing a mixture of 30.2 grams
of glacial acetic acid (EMD Chemicals, Darmstadt, Germany), 23.7
grams of formic acid (Alfa Aesar, Ward Hill, Mass.), 17.8 grams of
methoxy-ethoxy-ethoxy-acetic acid (MEEAA, Aldrich Chemical Company,
Milwaukee, Wis.), and 401.3 grams of deionized water using the same
process as described in the previous examples. The resulting
solution was then vacuum filtered in the same manner as previously
described. The filtered solution was then diluted with an
additional 500 grams of deionized water. This precursor solution
was then passed through the continuous hydrothermal reactor at a
flow rate of 10 ml per minute for a mean residence time of 48
minutes. The product material was later analyzed using transmission
electron microscopy. The particle size analysis is shown in Table
6.
Example 9
[0111] The aluminum-containing precursor for Example 9 was similar
to the precursor that was described in Preparatory Example 2 except
that lactic acid solution (about 9 grams or 0.1 mole, Aldrich
Chemical Company, Milwaukee, Wis.) was added to the product of the
digestion reaction. This solution was subsequently diluted with an
additional 500 grams of deionized water and then passed as the
feedstock through the continuous hydrothermal reactor at a flow
rate of 10 ml per minute for a mean residence time of 48 minutes.
The product material was later analyzed using transmission electron
microscopy. The particle size analysis is shown in Table 6.
TABLE-US-00006 TABLE 6 TEM Analysis of Examples 8 and 9 Ave. Median
Stand. Ave. Median Stand. Ave. Median Length Length Dev. Width
Width Dev. Aspect Aspect Stand. Ex. (nm) (nm) (nm) (nm) (nm) (nm)
Ratio Ratio Dev. 8 109.5 95.9 12.4 4.9 4.9 1.8 23.4 20.6 12.4 9
148.2 136.7 76.3 13.9 13.7 7.1 11.9 10.9 6.6
* * * * *